Pulsed oscillator



Oct. 11, 1949.

WITNESSES:

Filed June 15, 1946 INVENTOR Haydn L. Jackson.

ATTORNEY Patented Oct. 11, 1949 PULSED OSCILLATOR Hagan L. Jackson, Baltimore, Md., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application June 15, 1946, Serial No. 676,908

3 Claims.

My invention relates to electronic generators and in particular relates to generators adapted to produce pulses of high frequency waves, the waves of the pulse being of substantially con stant amplitude throughout the duration of each pulse. Such wave pulses have found many applications in the field of electronics, particularly during recent years; for example, they are widely used in radar systems now being employed extensively for military purposes.

The production of groups or pulses of high frequency waves, in which the maximum values of the individual waves embodied in the pulse are of substantially uniform amplitude, poses a problem of no small difficulty.

One object of my invention is, accordingly, to provide an electrical system capable of producing pulses of waves of substantially uniform amplitude.

Another object of my invention is to provide a novel system for producing electrical oscillations.

Still another object of my invention is to provide a novel circuit for electron tubes.

Still another object of my invention is to provide a novel type of electronic generator of electrical oscillations.

Other objects of my invention will become apparent upon reading the following description taken in connection with the drawings in which Figure l is a schematic diagram of one circuit adapted to carry out the principles of my invention; and

Fig. 2 is a graph showing the wave form of a pulse generator which is useful in explaining my invention.

In general, I produce pulses each embodying a plurality of waves of similar amplitude by providing an oscillation generator in which the plate voltage supply comprises successive pulses of voltage, the periodicity at which such pulses recur being equal to the number of pulses of waves desired from the output of the oscillation generator. The periodic frequency of the oscillation generator itself will, however, usually be considerably greater than the periodicity with which such plate voltage pulses are applied.

In order to produce the successive pulses impressed as plate voltage on the oscillation generator, I preferably employ an electron tube connected up in the form of a blocking oscillator.

Such blocking oscillator connections which may be employed are well known in the art, one being shown, for example, on page 514 of the Radio Engineers Handbook by Terman, first edition, 1943, McGraw-Hill Book Company, New York.

While such blocking oscillators readily produce voltage pulses occurring at desirable intervals, it has been found to be a matter of no small difiiculty to design such blocking oscillators so that the wave form which they impress on the anode of the high frequency generator is such as to cause the latter to generate pulses or groups of waves having uniform amplitude throughout the pulses. One difficulty which arises in this connection is the difiiculty of design and the costliness of any transformers which may be interposed between the blocking oscillator and the plate circuit of the oscillation generator which it is employed to supply. One of the important features of my invention is the discovery that by providing a proper impedance network in the circuits of the oscillation generator, it is possible to compensate for undesirable features in the wave form of the blocking oscillator, so that it is unnecessary for such blocking oscillator to be designed to produce voltage pulses of a particular or restricted form. In short, departure from the ideal wave form in the output of the blocking oscillator is compensated for and rendered of small consequence by providing the oscillation generator with a circuit network in accordance with the principles of my invention. For example, I have found that by connecting the control electrode circuit of the oscillation generator to earth through a resistor serially connected with a network comprising a capacitor shunted by a second resistor, departure of the voltage pulses of the blocking oscillator from a square-topped, straight-sided wave form are compensated for so that the oscillation generator produces pulses of waves which are of the same amplitude throughout the duration of each pulse.

Referring in detail to the drawings, the blocking oscillator which I employ comprises an electron tube I having a heated cathode connected to ground, a control electrode and an anode which is connected through a winding 2 of a transformer to the positive terminal of a direct-current voltage source having its negative terminal grounded. Cooperating with the winding 2 is 3' an inductively related secondary winding 3 shunted by a resistor 4. One terminal of the winding 3 is connected to the control electrode of the tube I, while the other terminal of the winding 3 is connected through a network comprising a capacitor 5 shunted by a variable resistor 6 to the cathode of the tube I. The cathode of the tube I is likewise connected through a third winding 1 inductively related to the winding 2, to the anodes of a pair of electron tubes.

8 and 9 having control electrodes, anodes and cathodes. The control electrodes of tubes 8 and 9 are respectively connected to two terminals of a Lecher wire system ll having a sliding member l2 which is connected to ground through a resistor l3 which is, in turn, connected in series with a network comprising a capacitor 14 shunted by a resistor 15. The cathodes of the tubes 8 and 9 are connected to leads IE, ll, [8 and I9 which pass centrally through a pair of conductors 2| and 22 having a length substantially equal to one-fourth of the wave-length which it is desired that the tubes 8 and 9 shall generate. The ends of tubes 2| and 22, which are remote from the cathodes of the tubes 8 and 9, are connected through substantially impedance-free grounds t earth. The ends of the conductors l6, l1, l8 and I9 which are remote from the tubes 8 and 9 are connected in multiple with each other to a source 23 of heating current. The terminals of the source 23 are bridged by a resistor 24 having a neutral point connected to earth through a second resistor 25. The ends of the tubes 2| and 22 are connected to the inleading wires to the cathodes of the tubes 9 and 9 through capacitors 26, 21, 2B and 29. Output lines 3| and 32 are connected respectively to variable taps on the conductors 2i and 22.

and causing current to flow through said cath- I odes, the resistors 24 and 25 and back to the grounded terminal of winding 1. During the intervals between the voltage pulses thus impressed by the winding 1, the tubes 8 and 9 produce no oscillations because their anodes are not sufficiently energized by voltage. During the pulses in which the winding 1 impresses positive voltage on the anodes of tubes 8 and 9, they are caused to generate electrical oscillations having a wave length equal to four times the length of one of the conductive cylinders 2| and 22. The slider l2 on the Lecher wires H is properly set to correspond with this wave length, and such oscillations continue throughout the duration of the positive pulse impressed by the winding 1 on the tubes 8 and 9.

The operation of the circuit shown in Fig. 1 may be considered with reference to Fig. 2. In Fig. 2 a curve A represents a pulse obtained from the winding 1 of the pulse transformer. This pulse has a curved top portion which may be of approximately 2 microseconds duration. The pulse also has a trailing edge which represents substantial voltage for approximately 15 microseconds. In radar applications such a trailing edge may materially limit the minimum range of the radar equipment.

For optimum performance of the oscillators 8, 9 it is desirable that a rectangular pulse be impressed on their anodes similar to that rcpresented by the dotted curve B. This pulse may have a width of approximately 2 microseconds and preferably has a flat top.

Production of the transformer output rep-resented by the curve A is due at least in part to a mismatch between the transformer and its load. Even if the transformer is properly matched with the load at the factory, a change of oscillator tubes or other components in the field may produce a mismatch. Furthermore, the provision of a proper match in the factory requires painstaking technique,

In accordance with the invention, the resistor l3 assists in producing a flat-top pulse. This resistor i not essential for determining the eifective pulse width.

The resistor l5 and capacitor 54 cooperate to determine the effective period of operation of the oscillator. When a pulse is produced, the capacitor charges to a value sufficient to cut off the oscillator. The time required for such charging may, for example, be of the order of 2 microseconds. The oscillator consequently operates as though energized by the rectangular pulse B of Fig. 2. Preferably the resistor it is proportioned to maintain the oscillator in cut-off condition for the period represented by the trailing edge of the pulse A. During this period the energy stored in the pulse transformer is suitably dissipated, as in the resistor 4.

From the foregoing discussion, it is clear that the invention provides performance comparable to that produced by the rectangular pulse B of Fig. 2. However, the invention substantially eliminates the necessity for maintaining a close match between the components of the system.

It should be noted that the number of tubes in the oscillator and the specific circuits employed therefor may be varied appreciably.

I claim as my invention:

1. In combination with an electron tube having an anode, a grounded cathode and a control electrode, means for impressing on the anode circuit of said tube pulses of positive voltage, and means for connecting said control electrode to ground through a network consisting of a resistor serially connected with a capacitor which is shunted by a second resistor.

2. In combination with two electron tubes each comprising an anode, a control electrode and a cathode, a quarter-wave conductor serially connected between each cathode and ground, a Lecher wire system interconnecting said control electrodes, a network interposed between the slider of said Lecher system and ground, comprising a resistor serially connected with a capacitor which is shunted by a second resistor, and means for impressing positive voltage pulses between the ground and the anodes of said tubes.

3. In combination with two electron tubes each comprising an anode, a control electrode and a cathode, a quarter-wave conductor serially connected between each cathode and ground, a Lecher wire system interconecting said control electrodes, a network interposed between the slider of said Lecher system and ground comprising a resistor serially connected with a capacitor which is shunted by a second resistor, and a third electron tube having a grounded cathode and an anode connected through a first transformer winding to a voltage source, a second transformer winding associated with said first transformer winding connected in series with a capacitor between the control electrode and cathode of said third electron tube, and a third transformer winding associated with the first said transformer winding and connected between ground and the UNITED STATES PATENTS Name Date Schlesinger Nov. 22, 1938 Archenbronn Dec. 11, 1945 Labin Sept. 24, 1946 Bradley Dec. 17, 1946 Hausy Aug. 19, 1947 Kentner Nov. 18, 1947 

